The invention relates to a container for a heat storage medium having in the solid state a density which varies in accordance with the heat content and being convertible from the solid to the fluid state and from the fluid to the solid state in order to store and release heat.
Heat storage means of this kind, wherein the physical condition of the heat storage medium changes between the fluid and solid state are also referred to as latent heat storage means. They have the advantage that the change in the heat content takes place at a substantially constant temperature, namely at the temperature at which the physical condition changes.
Latent heat storage means of this kind are used, for example, in heating systems where they assist the heating system during peak requirements and are recharged by the heating system in the event of low heat requirements.
Latent heat storage means containing Glauber's slat as the heat storage medium have been suggested. Glauber's salt changes from the solid to the fluid state at a temperature of 32.4.degree. C. and thereby releases heat in the amount of 357.3 Btu per liter.
When heat is removed from the heat storage medium, the latter cools down to its melting point and finally changes into the solid state. Upon further cooling down the volume of the solid medium can be decreased by, for example, compression or recrystallization. Conversely, heating of the solid medium results in a thermal expansion thereof until it changes to the fluid state upon arrival at the melting temperature.
The problem consists in the fact that a corresponding increase in the volume of the storage medium resulting from heating the latter has to be accommodated by the heat storage medium container. An increase in the volume cannot be equally distributed inside the container owing to the solid state of the medium, which destroys rigid container walls.
For this reason, heat storage containers of this kind have been made of plastic materials which are expandible and can therefore accommodate the increases in volume which occur. Plastic receptacles of this kind do, however, have the disadvantage that the expansions are not completely reversible and so residual expansion remains after each expansion. The numerous increases and decreases in volume which occur periodically inevitably result in a lasting enlargement of the container, which is not tolerable.